Figure 6. Effects of IGF signaling on the accumulation of oligodendrocyte progenitors. A, Oligodendrocyte progenitors (green), detected by NG2, accumulate with the demyelinating corpus callosum in wild-type (WT) mice, peaking at 4 weeks when demyelination is complete. However, oligodendrocyte progenitors only accumulate within the ventral (v) and dorsal (d) edges of the corpus callosum, with very few cells in the middle (m) region of the corpus callosum in ΔIgf1r mice. By 9 weeks, there is a dramatic reduction in the number of NG2+ oligodendrocyte progenitors within the corpus callosum of WT and ΔIgf1r mice. B, The mean and SEM bars for the number of NG2+ oligodendrocyte progenitors/mm2 throughout the entire depth of the corpus callosum are plotted. *.p < 0.01; **p < 0.05. C, Although a large number of NG2+ oligodendrocyte progenitors (green) proliferate, detected by an anti-KI-67 antibody (red), at 4 weeks within the demyelinated corpus callosum in wild-type mice (arrowheads indicate NG2+/KI-67+ cells), no proliferating NG2+ oligodendrocyte progenitors were observed in the demyelinated corpus callosum of ΔIgf1r mice at 4 weeks. Three nonadjacent sections from each of three different wild-type and ΔIgf1r mice were examined for proliferating NG2+ oligodendrocyte progenitors. D, Apoptotic [detected by TUNEL assay (red)] NG2+ oligodendrocyte progenitors (green) were observed within the middle region of the corpus callosum in ΔIgf1r mice at 4 weeks (arrowhead indicates apoptotic NG2+ cells), whereas no apoptotic progenitors were detected in wild-type mice. Three nonadjacent sections from each of three different wild-type and CaMKIIα-cre/Igf1rΔflox/- mice were examined for apoptotic NG2+ oligodendrocyte progenitors. Scale bars: A, 50 μm; C, 15 μm; D, 10 μm.